Managing classroom lateness

I am a trainee teacher working mostly with 16-19 year olds.

I have recently observed a few lessons that were timetabled for 2hrs. In reality this is 1hr 50 mins to allow for 20mins breaks at the end & start of next 2hr lesson.

With a strict college classroom refreshment policy, I would contend these are long sessions for optimum learning outcomes. Being a mature student myself, I know my attention and retention abilities are stretched when I attend 2hr lessons without a chance to energise the brain.

Are we not exposing students to regular mental disgestion with these practices? I welcome others thoughts and ideas on the subject?